Smart contracts are programs deployed on blockchains that run upon meeting predetermined conditions. Once deployed, smart contracts are immutable, thus, defects in the deployed code cannot be fixed. As a consequence, software engineering anti-patterns, such as code cloning, pose a threat to code quality and security if unnoticed before deployment. In this paper, we report on the cloning practices of the Ethereum blockchain platform by analyzing 33,073 smart contracts amounting to over 4MLOC. Prior work reported an unusually high 79.2% of code clones in Ethereum smart contracts. We replicate this study at the conceptual level, i.e., we answer the same research questions by employing different methods. In particular, we analyze clones at the granularity of functions instead of code files, thereby providing a more fine-grained estimate of the clone ratio. Furthermore, we analyze more complex clone types, allowing for a richer analysis of cloning cases. To achieve this finer granularity of cloning analysis, we rely on the NiCad clone detection tool and extend it with support for Solidity, the programming language of the Ethereum platform. Our analysis shows that most findings of the original study hold at the finer granularity of our study as well; but also sheds light on some differences, and contributes new findings. Most notably, we report a 30.13% overall clone ratio, out of which 27.03% are exact duplicates. Our findings motivate improving the reuse mechanisms of Solidity, and in a broader context, of programming languages used for the development of smart contracts. Tool builders and language engineers can use this paper in the design and development of such reuse mechanisms. Business stakeholders can use this paper to better assess the security risks and technical outlooks of blockchain platforms.

In recent years,Pythonhas experienced an explosive growth in adoption, particularly among open source projects. WhilePython's dynamically-typed nature provides developers with powerful programming abstractions, that same dynamic type system allows for type-related defects to accumulate in code bases. To aid in the early detection of type-related defects, type annotations were introduced into thePythonecosystem (i.e., PEP-484) and static type checkers likemypyhave appeared on the market. While applying a type checker likemypycan in theory help to catch type-related defects before they impact users, little is known about the real impact of adopting a type checker to reveal defects inPythonprojects. In this paper, we study the extent to whichPythonprojects benefit from such type checking features. For this purpose, we mine the issue tracking and version control repositories of 210Pythonprojects on GitHub. Inspired by the work of Gaoet al.on type-related defects in JavaScript, we add type annotations to test whethermypydetects an error that would have helped developers to avoid real defects. We observe that 15 percent of the defects could have been prevented bymypy. Moreover, we find that there is no significant difference between the experience level of developers committing type-related defects and the experience of developers committing defects that are not type-related. In addition, a manual analysis of the anti-patterns that most commonly lead to type-checking faults reveals that the redefinition ofPythonreferences, dynamic attribute initialization and incorrectly handled Null objects are the most common causes of type-related faults. Since our study is conducted on fixed public defects that have gone through code reviews and multiple test cycles, these results represent a lower bound on the benefits of adopting a type checker. Therefore, we recommend incorporating a static type checker likemypyinto the development workflow, as not only will it prevent type-related defects but also mitigate certain anti-patterns during development.

Differential Evolution (DE) and Particle Swarm Optimization (PSO) algorithms are two commonly employed techniques in designing maximum power point tracking systems in photovoltaic (PV) farms. A mathematical formulation of the objective function is derived by implementing the maximum power theorem for load matching using the relationship between input and output impedances. This paper also proposes a novel Center-based Latin Hypercube (CLHS) initialization scheme for population-based algorithms; it is shown that for population initialization, the newly proposed technique of CLHS gives better results with a small population size. A comprehensive comparative study is conducted on DE and PSO algorithms in terms of control parameters, search components, and population initialization methods to determine the best algorithm with its corresponding optimal parameters settings and population initialization to solve a family of maximum power point tracking problems. The work shows that both algorithms are capable of tracking the maximum power point although the PSO is more effective over a small population size. In this study, in overall, 15,876 and 96,228 settings possibilities for DE and PSO respectively are investigated.